Static die necking is a process whereby the open ends of can bodies are provided with a neck of reduced diameter utilizing a necking tool having reciprocating concentric necking die and pilot assemblies that are mounted within a rotating necking turret and movable longitudinally under the action of a cam follower bracket to which the necking die assembly is mounted. The cam follower bracket thereby rotates with the turret while engaging a cam rail mounted adjacent and longitudinally spaced from the rear face of the necking turret. A can body is maintained in concentric alignment with the open end thereof facing the necking tool of the concentric die and pilot assemblies for rotation therewith. The reciprocating pilot assembly is spring loaded forwardly from the reciprocating die member. The forward portions of the die member and pilot assembly are intended to enter the open end of the can body to form the neck of the can.
More specifically, the die member is driven forwardly and, through its spring loaded interconnection with the pilot assembly, drives the pilot assembly forwardly toward the open end of the can. The outer end of the pilot assembly enters the open end of the can in advance of the die member to provide an anvil surface against which the die can work. The forward advance of the pilot assembly is stopped by the engagement of a homing surface on the necking turret with an outwardly projecting rear portion of the pilot assembly, slightly before the forward portion of the die member engages the open end of the can. As the die member continues to be driven forwardly by the cam, its die forming surface deforms the open end of the can against the anvil surface of the pilot assembly to provide a necked-in end to the can body.
A necking machine of the type discussed above is disclosed, for example, in U.S. Pat. Nos. 4,457,158 and 4,693,108. In the latter '108 patent, each necking station also has a container pressurizing means in the form of an annular chamber formed in the pilot assembly which acts as a holding chamber prior to transmitting the pressurized fluid into the container from a central large reservoir located in the necking turret. In the type of static die necking discussed above to which the present invention pertains, pressurized fluid internally of the container is critical to strengthen the column load force of the side wall of the container during the necking process. There are particular problems inherent in introducing sufficient pressurized fluid into the container as the speed of production is increased.
It is accordingly one object of the present invention to enable rapid pressurization of the container body interior by air flowing to it through the pilot assembly shaft.
Another object is to rapidly pressurize the can interior to sustain high peak necking loading without crushing by placing a large volume reservoir in the necking spindle assembly immediately adjacent the can interior.
Still another object is to substantially instantaneously flow pressurized air from the reservoir into the can interior through a valve means having large diameter inlet ports communicating between the reservoir and can interior.